Current sensors which measure a flow of a current are divided according to current measurement methods, i.e., a direct measurement method which has a resistance arranged at a point where a current flows, and measures a current value through a voltage, and an indirect measurement method which measures a current value through a magnetic field generated by a flow of a current.
Due to power consumption by a resistance and interference in the flow of a current, the indirect measurement method is preferred to the direct measurement method.
However, in the case of the indirect measurement method, a magnetic field generated by a disturbance is included in addition to a magnetic field generated by a current to be measured as shown in FIG. 1.
Accordingly, to prevent the magnetic field generated by the disturbance, a magnetic field shielding film may be installed in a current sensor. However, this becomes a factor that increases both the volume and the price of a current sensor module.
In addition to the disturbance, there is an offset as a factor causing an error in the current sensor. The offset of a sensor is generated due to non-uniformity in a sensor fabrication process, and may correspond to a voltage value outputted in the absence of a sensor input. The concept of the offset is illustrated in FIG. 2.
A current sensor using the indirect measurement method may use a magneto resistance (MR) effect that a resistance value is changed according to a size of a magnetic field. An MR sensor is a sensor which has an electric resistance changed according to a magnetic field, and includes an anisotropic magneto resistance (AMR) sensor, a giant magneto resistance (GMR) sensor, a tunnel magneto resistance (TMR) sensor, an extraordinary magneto resistance (EMR), a planar hall resistance (PHR) sensor, or the like.
FIG. 3 illustrates a PHR sensor of a ring shape which is a kind of an MR sensor, and an electric equivalent circuit.
The PHR sensor of the ring type uses a principle that a resistance value (R1, R2, R3, and R4) changes according to directions of a bias current and an external magnetic field. As shown in FIG. 4, the bias current I and the external magnetic field B have opposite directions at R1 and R3 and have the same directions at R2 and R4. Accordingly, when the resistance values of R1 and R3 increase, the resistance values of R2 and R4 decrease.
As described above, in a current sensor of a Wheatstone bridge type like the PHR sensor, diagonally opposite resistances change in the same direction as each other. When R1×R3=R2×R4, the output voltage of the Wheatstone bridge type sensor is 0V and an offset does not occur. That is, the offset disappears when the products of opposite resistances are equal to each other.
However, in practice, it is impossible to fabricate a PHR sensor to satisfy equation R1×R3=R2×R4, and thus the PHR sensor unavoidably suffers from an offset. Accordingly, a voltage is outputted from output nodes (2 and 4) of the PHR sensor when the bias current I is applied although there is no magnetic field generated by an external current.
As described above, a disturbance and an offset are the factors that cause an error in a sensor, and various technologies are suggested to remove these factors. However, most of the technologies remove only one of the disturbance and the offset.
Accordingly, there are disadvantages that two types of correction circuits, i.e., a disturbance correction circuit and an offset correction circuit, are required, and thus complexity increases, an area/volume increases, and much time is required to correct.